A few years back, Ordnance Survey Ireland digitised their map archive and made it available on a subscription website, www.irishhistoricmaps.ie The site included complete sets of the earliest 6 to the mile series produced between 1837 and 1842, in both the original black-and-white and beautiful hand-coloured versions, as well as the much more detailed 25 to the mile series produced between 1888 and 1913. Although the site was paying, charging between 5 for a day and 300 for a year, access was free through any public library.

Despite the great care that went into the digitisation and the site, it was not a commercial success. Perhaps, like so many before them, OSI overestimated the potential of the Irish-American market. Perhaps the map-viewer was too much for low-quality broadband connections. In any case, the site did not achieve what was expected of it.

To OSIs credit, they have picked themselves up and moved on. The entire set of their historic maps is now available to browse for free at the Ordnance Survey on-line shop at maps.osi.ie, and in a format that is just wonderful. Starting from the entire island, you can zoom right in to the 25 scale, overlay it with a transparent modern street-level map, toggle back and forth between the 1830s and the 1890s, between the colour and black-and-white versions, search for place-names It can very easily become addictive.

There are some limitations: the 25 maps for areas now in Northern Ireland seem to be missing (though there are excellent map searches for Northern Ireland place-names at www.placenamesni.org and at the Northern Ireland Ordnance Survey,) and the on-screen maps are peppered with OSI watermarks, because the Survey is still selling high-quality print versions. But even with these restrictions, the site is now a superb research tool for examining in detail the evolution of every single field and street on the island.